/*
 * Copyright (C) 2007 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import java.util.Map;

import javax.annotation.Nullable;

import com.google.common.annotations.GwtCompatible;

/**
 * An object representing the differences between two maps.
 * 
 * @author Kevin Bourrillion
 * @since 2010.01.04 <b>stable</b> (imported from Google Collections Library)
 */
@GwtCompatible
public interface MapDifference<K, V> {
    /**
     * Returns {@code true} if there are no differences between the two maps;
     * that is, if the maps are equal.
     */
    boolean areEqual();

    /**
     * Returns an unmodifiable map containing the entries from the left map
     * whose keys are not present in the right map.
     */
    Map<K, V> entriesOnlyOnLeft();

    /**
     * Returns an unmodifiable map containing the entries from the right map
     * whose keys are not present in the left map.
     */
    Map<K, V> entriesOnlyOnRight();

    /**
     * Returns an unmodifiable map containing the entries that appear in both
     * maps; that is, the intersection of the two maps.
     */
    Map<K, V> entriesInCommon();

    /**
     * Returns an unmodifiable map describing keys that appear in both maps, but
     * with different values.
     */
    Map<K, ValueDifference<V>> entriesDiffering();

    /**
     * Compares the specified object with this instance for equality. Returns
     * {@code true} if the given object is also a {@code MapDifference} and the
     * values returned by the {@link #entriesOnlyOnLeft()},
     * {@link #entriesOnlyOnRight()}, {@link #entriesInCommon()} and
     * {@link #entriesDiffering()} of the two instances are equal.
     */
    boolean equals(@Nullable Object object);

    /**
     * Returns the hash code for this instance. This is defined as the hash code
     * of
     * 
     * <pre>
     * {@code
     * 
     *   Arrays.asList(entriesOnlyOnLeft(), entriesOnlyOnRight(),
     *       entriesInCommon(), entriesDiffering())}
     * </pre>
     */
    int hashCode();

    /**
     * A difference between the mappings from two maps with the same key. The
     * {@code leftValue()} and {@code rightValue} are not equal, and one but not
     * both of them may be null.
     */
    interface ValueDifference<V> {
        /**
         * Returns the value from the left map (possibly null).
         */
        V leftValue();

        /**
         * Returns the value from the right map (possibly null).
         */
        V rightValue();

        /**
         * Two instances are considered equal if their {@link #leftValue()}
         * values are equal and their {@link #rightValue()} values are also
         * equal.
         */
        @Override
        boolean equals(@Nullable Object other);

        /**
         * The hash code equals the value
         * {@code Arrays.asList(leftValue(), rightValue()).hashCode()}.
         */
        @Override
        int hashCode();
    }

}
